The present invention is directed to integrated circuits and their processing for the manufacture of electronic devices. More particularly, the invention provides a method for manufacturing an electrode structure for a liquid crystal on silicon (“LCOS”) device for displays. But it would be recognized that the invention has a much broader range of applicability.
Electronic display technologies have rapidly developed over the years. From the early days, cathode ray tube technology, commonly called CRTs, outputted selected pixel elements onto a glass screen in conventional television sets. These television sets originally output black and white moving pictures. Color television sets soon replaced most if not all black and white television units. Although very successful, CRTs were often bulky, difficult to make larger, and had other limitations.
CRTs were soon replaced, at least in part, with liquid crystal panel displays. These liquid crystal panel displays commonly called LCDs used an array of transistor elements coupled to a liquid crystal material and color filter to output moving pictures in color. Many computer terminals and smaller display devices often relied upon LCDs to output video, text, and other visual features. Unfortunately, liquid crystal panels often had low yields and were difficult to scale up to larger sizes. These LCDs were often unsuitable for larger displays often required for television sets and the like.
Accordingly, projection display units have been developed. These projection display units include, among others, a counterpart liquid crystal display, which outputs light from selected pixel elements through a lens to a larger display to create moving pictures, text, and other visual images. Another technology is called “Digital Light Processing” (DLP), which is a commercial name from Texas Instruments Incorporated (TI) from Texas, USA. DLP is often referred to as the use of “micro-mirrors.” DLP relies upon a few hundred thousand tiny mirrors, which line up in 800 rows of 600 mirrors each. Each of the mirrors is hinged. An actuator is attached to each of the hinges. The actuator is often electrostatic energy that can tilt each of the mirrors at high frequency. The moving mirrors can modulate light, which can be transmitted through a lens and then displayed on a screen. Although DLP has been successful, it is often difficult to manufacture and subject to low yields, etc.
Yet another technique is called LCOS. LCOS uses liquid crystals applied to a reflective mirror substrate. As the liquid crystals “open” or “close,” light is reflected or blocked, which modulates the light to create an image for display. Compared to the conventional transmissive LCD, a reflective LCOS display allows more light to be passed through the optics and therefore it provides a higher luminance.
As indicated in FIG. 1, aluminum is often used as the reflective film for electrodes. To get high reflectivity, a smooth aluminum/oxide structures is often needed. The conventional method to smooth the aluminum/oxide is chemical mechanical planarization, commonly called the Al CMP process. However, CMP process, however, causes many issues, such as dishing, micro-scratching and oxidation of the Al surface. These and other limitations are described in greater detail below.
From the above, it is seen that an improved technique for processing devices is desired.